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Area forecast discussion 
National Weather Service Des Moines Iowa
1044 PM CDT Tuesday Sep 1 2015

Short term /tonight/...
issued at 316 PM CDT Tuesday Sep 1 2015

Weak upper level disturbance currently moving through South Dakota/NE to
continue push eastward through Iowa overnight. Push of Theta-E
advection into western County Warning Area by late evening and spreading eastward
late tonight. Low level jet increases and becomes oriented into the state with
the moisture push...which will aid in showers/storm development to
the west this evening. Hi-res models similar in thinking with a line
of storms becoming more north-S oriented moving through the County Warning Area late
tonight. Best forcing to be across the northern/western County Warning Area and into
southern Minnesota. Therefore have the highest probability of precipitation in that region.
Instability OK so continued with the mention of thunder...but shear
not great so severe storms are not anticipated. Fz level quite high as
well...with higher precipitable waters around 1.6 so expect possibility of brief
heavy rainfall within a stronger storm. Otherwise dewpoints in the
70s across the area...with southerly flow continuing through the
night...so expect lows to remain higher in the upper 60s to low 70s.

Long term /Wednesday through Tuesday/...
issued at 316 PM CDT Tuesday Sep 1 2015

Fairly quiet weather during the extended with the main concern
focused on temperatures as a large upper level ridge holds in
place through the weekend. Some timing and location concerns with respect to a
few weak shortwaves riding the 500mb ridge...but no significant
precipitation until early next week. Leaned toward a blend of the
European model (ecmwf)/NAM through Friday...then placed more weight toward the
European model (ecmwf) during the extended.

Wednesday into Friday...a weak shortwave and vorticity maximum cut across
southern Minnesota with the trough extending south into Iowa during
the day Wednesday. Broad and weak forcing for ascent stretches from
southwest to northeast Iowa Wednesday as the trough moves east...the
forcing wanes and confines to just northeast Iowa by the afternoon
hours. Have slight probability of precipitation going oriented with the aforementioned axis
through 18z Wednesday...then across the northeast through the
afternoon and evening hours. System is slower to move east of the
forecast area and kept in probability of precipitation through 06z Thursday in the
northeast. Low confidence with much quantitative precipitation forecast tomorrow with the lack of
significant moisture and forcing available. Another weak upper level
shortwave looks to scrape the far southwest early Thursday...but
models continue to track it further south and left forecast dry
at this time. Otherwise...warm and humid conditions continue through the end
of the work week...but heat index values remain below heat advisory
levels.

Saturday through Monday...large upper level ridge continues to bring
warm and humid conditions through weekend. Another weak shortwave
rides the ridge late Saturday night into Sunday and looks to provide
western to northwestern portions of the forecast area with some
thunderstorm chances. However...the next best potential for rainfall
is late Sunday night into Monday as a fairly strong and deep trough
develops over the northern rockies and pushes across the Dakotas
into Minnesota Sunday into Monday. The cold front associated with
this system looks to be the main focus for thunderstorm activity
late Sunday night into Monday morning. Surface high and cold air advection move
into the state Monday afternoon and trended dry past 00z Tuesday
with both GFS/European model (ecmwf) dry during this time.

&&

Aviation...02/06z
issued at 1043 PM CDT Tuesday Sep 1 2015

Best forcing remains north across Minnesota...but another area of weaker
warm air advection developing some showers across SW Iowa. Have
updated timing of shower activity across area through 18z Wednesday...
after 18z most of the showers will be east of area. VFR ceilings
expected with some MVFR br overnight north. Otherwise...winds mix
after 16z most areas with gust potential to 23kt diminishing by 00z
with VFR conditions and light winds expected through end of
period. /Rev

&&

Dmx watches/warnings/advisories...
none.
&&

$$

Short term...beerends
long term...podrazik
aviation...rev

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